Segfault with use_combined_no_overlap due to uninitialized FixedCapacityVector in CombinedDisjunctive

[fgregg]

What version of OR-Tools and what language are you using?
Version: v9.15
Language: Python 3.13

Which solver are you using (e.g. CP-SAT, Routing Solver, GLOP, BOP, Gurobi)
CP-SAT

What operating system (Linux, Windows, ...) and version?
macOS 15 (arm64)

What did you do?

Set solver.parameters.use_combined_no_overlap = True on a model with a NoOverlap constraint containing 3 or more intervals.

from ortools.sat.python import cp_model

model = cp_model.CpModel()
starts = [model.new_int_var(0, 100, f"s_{i}") for i in range(3)]
intervals = [model.new_fixed_size_interval_var(starts[i], 10, f"iv_{i}") for i in range(3)]
model.add_no_overlap(intervals)

solver = cp_model.CpSolver()
solver.parameters.use_combined_no_overlap = True
status = solver.solve(model)

What did you expect to see

A solved model (OPTIMAL or FEASIBLE status).

What did you see instead?

Segmentation fault during solve().

Fatal Python error: Segmentation fault

Thread 0x0000000208402240 (most recent call first):
  File ".../ortools/sat/python/cp_model.py", line 1771 in solve

Models with 2 or fewer intervals work fine (the CombinedDisjunctive code path requires intervals.size() > 2 in AddDisjunctive). Also reproduces with optional intervals (new_optional_fixed_size_interval_var).

Anything else we should know about your project / environment

The bug is a null pointer write in CombinedDisjunctive::AddNoOverlap (ortools/sat/disjunctive.cc, line 341). The FixedCapacityVector backing a TaskSet is default-constructed with data_ = nullptr, and ClearAndReserve() is never called. During Propagate(), TaskSet::AddEntry() calls push_back() which writes to the null pointer.

Suggested fix — allocate storage before constructing the TaskSet:

 template <bool time_direction>
 void CombinedDisjunctive<time_direction>::AddNoOverlap(
     absl::Span<const IntervalVariable> vars) {
   const int index = task_sets_.size();
-  task_sets_.emplace_back(task_set_storage_.emplace_back());
+  auto& storage = task_set_storage_.emplace_back();
+  storage.ClearAndReserve(vars.size());
+  task_sets_.emplace_back(storage);
   end_mins_.push_back(kMinIntegerValue);
   for (const IntervalVariable var : vars) {
     task_to_disjunctives_[var.value()].push_back(index);
   }
 }

Verified fix locally by building from source.